Haas Mini run 4th axis at constant speed during program

Hello all I am trying to run a 4th axis on a Haas mini mill and it is working fine if I wanted to run it in a traditional way, angular increments. However we are using this to preshape aspheric lenses for diamond turning. Currently all of our shaping equipment can only generate spheres so I plan to use the mill to program and aspheric curve and cut the blank while the 4th axis constantly rotates and simply running a 2D path. I am hoping there is a good way to do this within Gcode that I am unaware of or in Mcode if need me. It is much simpler and more accurate to generate these curves in a 2d path than trying to import step files with a complex surface on them.

Otherwise, I imagine Haas systems are not open enough but hooking up to a seperate controller entirely is a possibility if I can get the enough info about the wiring.

Best option I can think of so far is adding a custom Mcode to every line and changing the angular increment per line in the mcode to, in a way, set the rotation speed.

This will be 95% of what we use this axis for and I would like to keep is as simple as possible for operators to create new programs themselves. Also considering selling the 4th axis and buying a worm gearbox and a simple motor to replace it at this point. My hope was that I could command M3 H4 F50 for example(M3(Spindle on) H4(Motor drive 4) F50(50RPM) but it seems there is no motor select command in M3.

The rotary is controlled by G code commands for it as the "A" axis. Example starting at A0. and going to A360. will get you one revolution. But, you can't just tell it to keep going. There is also a limit of how many rotations you can do before it needs to "rewind." I believe it is 9,999 degrees or just over 27 full rotations.

In most application that is just fine, but in yours that probably will not work.

My manual for the 4th axis also claims 9,999 degrees. However it'll go 154,000 degrees. Easy to check. MDI: G0 A154000.
If it even starts it'll do it.
As far as the tool path, I've done this a few times. My CAM wanted to post many many steps for a simple path. I just found the curve and posted it out and then added the A axis rotational moves. It was a single curve so I'm not sure it'll work easily with your aspheric curve (I had to google it lol)

Yeah the gearbox is getting more and more tempting, if only the purchase approval process wasn't so daunting around here.

I was worried about the angular limits being an issue and indeed when the program is done it has to rewind fully. This program is currently just about 3,000 degrees though so this is manageable. I tried the "G00 G92 G28 A0" manually to unwind and that worked so I will add that to the end of the program and hopefully I can go to 154,000 like Chris said and then get around unwinding. This should work for now I suppose. It is definitely frustrating that this is not more readily achievable though.

quck rotary G28

Yeah the gearbox is getting more and more tempting, if only the purchase approval process wasn't so daunting around here.

I was worried about the angular limits being an issue and indeed when the program is done it has to rewind fully. This program is currently just about 3,000 degrees though so this is manageable. I tried the "G00 G92 G28 A0" manually to unwind and that worked so I will add that to the end of the program and hopefully I can go to 154,000 like Chris said and then get around unwinding. This should work for now I suppose. It is definitely frustrating that this is not more readily achievable though.

I worked with pre shaping lenses for 8 years up till this summer. We had a glass aspheric lens that was being quoted and this was an idea of how to run it. But didn't end up doing that job, but regardless every lens we made which was a lot, was done with 3d tool paths and simple to complex work holding. The main thing is to leave material on all surfaces and diamond turn it to final size. This way you can make soft jaws or glue or vacuum chucks to hold the parts prior to diamond turning.

And if you need to make mods to lens shape such as adding a flange or whatever to hold it in mill then giver as the time it takes to diamond turn off a small lip or flange or whatever is miniscule compared to having to buy and setup a rotary.

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